Light printing even with new ribbon

I have two printers, Pansonic both, KX-P1624 and KX-P2123 (I think), both printers will not print to the paper even with new ribbons. It acts like they are printing and occasionally the 1624 will print so light you can hardly see it. The 2123 was printing fine when paper got jammed and that is when the problem started. Could it be in the serial/parallel cord (don't know what it is called)? I've tried different computers, both desktop. The program I am trying to print from is CLS, Client Ledger System, an accounting program. Any help you could give me would be appreciated so much. Mary Rodgers